1. Field of the Invention
The invention is directed generally to information networks and more specifically to a method and circuit arrangement for controlling the transmission of information for interactive services.
2. Description of the Related Art
Coaxial networks via which analog information signals in the form of video signals are transmitted to the respective subscriber are used for contemporary cable television applications. The transmission occurs via a uniform channel grid into which the video signals are inserted. Information signals of various narrowband--or broadband--services such as, for example, telephony, interactive video on call (video on demand) or other interactive video services (tele-shopping, tele-education, etc.) can also be transmitted via these coaxial networks that are already in place.
Thus, a need has arisen for providing these information signals for example, as ATM information signals available to all subscribers in the uniform channel grid under discussion.
FIG. 1 shows an example of a prior art network structure on which such a procedure is implemented. As illustrate, a coaxial network KN having the usual tree structure is shown to the left of a hand end (connection unit CU), whereby the transmission of the information signals occurs optically or electrically. The optical transmission medium is respectively identified with a circle, whereas the electrical transmission cable drawn with thicker lines is not referenced. Further, an optical conveyer means OCC is shown that assures that electrical information signals are converted into optical information signals and vice versa. At the subscriber side, the coaxial network KN is provided with a plurality of network termination apparatus NT/A that can be set top boxes. FIG. 1 shows only one NT/A for simplicity.
The purpose of the NT/A is to modify the received or, respectively, the sent information signals to enable a connection of traditional terminal equipment. By way of example, FIG. 1 shows such terminal equipment RF,CPE/A and T. The terminal equipment RF is a standard television set, the terminal equipment CPE/A is an ATM terminal device such as, for example, a computer or a work station, and the terminal equipment T is an analog or digital telephone. The distribution TV signals are transmitted in analog form in the coaxial network KN. The signals are supplied via a TV into the connection unit CU and are supplied from the latter to all connected subscribers via the coaxial network KN. The video signals can then be received in a known way by the video receiver RF connected to a network termination apparatus NT/A.
As illustrated in FIG. 1, ATM information signals are bidirectionally transmitted. The signals are supplied, for example, by a service means designed as a video server VS connected to the connection unit CU via an ATM switching device ATMS, whereby the control of these events is undertaken by a central control means TMN. It has been proposed to transmit the ATM information signals in narrow channels corresponding to the channel grid for TV applications.
FIG. 2 shows a possibility of how such a transmission can be implemented. The transmission of the analog information signals occurs in a frequency range B.sub.1 between 50 and 450 MHz in the form of video signals for cable television applications. Each video signal occupies channel with a bandwidth of 8 MHz. The digital downstream or, respectively, upstream signals of the interactive services are then inserted into this channel grid of 8 MHz above the television band. The downstream signals are thereby transmitted, for example, in a frequency band B.sub.2 between 450 and 750 MHz and the upstream signals are transmitted in a frequency band B.sub.3 between 750 and 1000 MHz. This procedure, however, requires an allocation of the information signals provided for a specific subscriber to specific transmission channels of the channel grid. In general, this allocation is implemented by a central control computer of the network control center TMN in combination with the local control devices SEC of the connection unit CU and the network termination apparatus NT/A. The status and control information required for this purpose, however, must thus be deposited in a table provided for this purpose in the central control computer of the network control center TMN. Before setting up a connection to a server, a subscriber must thus receive the corresponding information from this computer in order to set the reception means of the network termination apparatus NT/A to the corresponding channels.
A problem with such a procedure, however, is that the central control computer of the network control center is subject to a very high load, and the outlay is correspondingly high.